A stereomicroscope, such as a surgical microscope, has provided an operator with magnified observation images of an affected part in a surgical operation relative to neurosurgery, otolaryngology, ophthalmology, etc., and has played an important role in the improvement of surgical efficiency. In recent years, not only the magnified observation images of the affected part obtained by the stereomicroscope, but also a tomographic image including the surroundings of the affected part, produced by computer aided tomography (CAT) imaging, magnetic resonance (MR) imaging, or ultrasonic imaging, and endoscope observation imaging have come into use in order to plan a surgical operation as well as to perform the surgical operation. Each of these individual imaging types provide useful information when viewed alone. However, greater benefits are achieved when two or more types of images are simultaneously presented to the viewer so that comparisons between the images may be made. In this way, additional information can be provided to the operator as compared to that which is available from viewing the separate images alone.
Thus, it is desired that a stereomicroscope allow an operator to observe, for example, a CAT or MR image and an endoscope observation image simultaneously with the stereomicroscope observation images while looking into the stereomicroscope eyepieces. Stereomicroscopes having this capability are disclosed in Japanese Laid Open Patent Applications S62-166310 and H10-333047.
The stereomicroscope as set forth in Japanese Laid Open Patent Application S62-166310 has an electronic image display means for displaying images (i.e., electronic images) and image projection optical systems for conducting these images to eyepiece optical systems. The eyepiece optical systems are shared so that the electronic images are viewed within the field of view of the stereomicroscope observation image. This publication, however, does not in any way suggest a problem relative to the movement of the eyepiece optical systems caused by the interpupillary adjustment of a stereomicroscope. Nor does this publication suggest a solution to this problem that is solved by the present invention. "Interpupillary adjustment" refers to adjusting the spacing between the left and right eyepieces of the stereomicroscope in order to conform the spacing to the distance between the left and right pupils of an observer. An interpupillary adjustment mechanism is commonly used with stereomicroscopes to account for the variability in interpupillary distance among different observers.
Using the technique described in Japanese Laid Open Patent Application S62-166310 to perform interpupillary adjustment, the electronic image display means and the image projection optical systems must be moved integrally with the eyepiece optical systems. This is required because the images on the electronic image display means are projected in accordance with the movement of the eyepiece optical systems due to interpupillary adjustment. Thus, a sufficient space for moving the electronic image display means and projection optical systems in the housing of the stereomicroscope is required, causing the housing to be larger than otherwise needed. In a stereomicroscope such as a surgical microscope, compactness of the entire microscope is indispensable for improved work efficiency. However, with the technique described in Japanese Laid Open Patent Application S62-166310, achieving compactness is impossible.
On the other hand, in the stereomicroscope disclosed in Japanese Laid Open Patent Application H10-333047, each image projection optical system is divided into a collimating optical system and an imaging optical system. An arrangement is made so that only the imaging optical system is moved integrally with an eyepiece optical system in accordance with the interpupillary adjustment in order to always receive an image beam that emerges from a collimating optical system. An electronic image display means remains fixed with respect to the interpupillary adjustment, but the displayed electronic image is projected in accordance with the movement of the eyepiece optical system so that the stereomicroscope observation image and the projected electronic image can be observed simultaneously. Thus, a portion of the image projection optical system is moved during interpupillary adjustment, and a space is required for this movement. Therefore, a larger size housing is again required as compared to the housing size that would be needed if there were no movement of a portion of the image projection system during interpupillary adjustment, and optimum compactness is again not achieved.